Field of the Invention
Embodiments of the present invention relate generally to a stimulation tool. More specifically, the embodiments relate to stimulation tools with a plurality of sleeves capable of being actuated by a single actuating members.
Description of the Related Art
During hydraulic fracturing operations, operators want to minimize the number of trips needed to run in a well and simultaneously optimize the placement of stimulation treatments and rig/fracture equipment. Therefore, operators prefer to use a single-trip, multistage fracing system to selectively stimulate multiple stages, intervals, or zones of the wellbore. Typically, multistage fracing systems have a series of packers along a tubing string to isolate zones in the well. Interspersed between the packers along the tubing string are ports and isolation tools with sliding sleeves capable of allowing fluid communication through the ports. The sliding sleeves are initially closed, but can be opened to stimulate the various zones along the tubing string.
Traditionally, operators rig up fracturing surface equipment and apply pressure to open a sliding sleeve on an end of the tubing string. Then, a first zone is treated. Each remaining unopened sliding sleeve in the isolation tools further uphole is subsequently actuated such that fluid is diverted to flow out of the tubing string and to fracture the zones along the tubing string. The actuation of the sliding sleeves must be performed in a sequential manner to allow the borehole to be progressively fractured along the length of the bore, without leaking fracture fluid out through previously fractured regions.
Due to the expense and frequent failure of electrical devices downhole, the most common approach to actuate the sliding sleeves is mechanical. For example, successive zones are treated by dropping successively increasing sized balls down the tubing string. Each ball opens a corresponding sleeve such that each individual zone can be accurately stimulated.
The sliding sleeves are configured such that the first dropped ball, which has the smallest diameter relative to the other balls, passes through at least one sliding sleeve having a ball seat larger than the first ball. The first ball continues down the tubing string until the first ball reaches the sliding sleeve furthest downhole. The sliding sleeve furthest downhole is configured to have a ball seat smaller than the first dropped ball such that the first ball seats at the sliding sleeve to block a bore of the tubing string and cause a port to open. As a result, the first ball in the sliding sleeve diverts fluid flow into the formation adjacent the port.
Subsequently, balls of increasing size are dropped into the tubing string such that the balls pass through the nearest sliding sleeves but seat at a sliding sleeve further downhole having a suitably sized seat. As is typical, the dropped balls engage respective seat sizes in the sliding sleeves and create barriers to the zones below. Applied differential tubing pressure then moves the sliding sleeve to expose the port such that treatment fluid may stimulate the zone adjacent the port. This process may be repeated until all of the sliding sleeves have been actuated in the order of furthest downhole to nearest the surface.
Although dropping balls of increasing size to actuate sliding sleeves remains a common technique for stimulation, this approach has a number of disadvantages. First, practical limitations restrict the number of zones that can be stimulated in the tubing string. For example, because the zones are treated in stages, the smallest ball and corresponding ball seat are used for the sliding sleeve furthest downhole. Sliding sleeves nearer to the surface have successively larger seats for larger balls. As a result, the number of sliding sleeves that may be used is limited by the dimensions of the tubing string and ball seat sizes.
Another disadvantage of conventional stimulation techniques is that the ball seats act as undesirable restrictions to fluid flow through the tubing string. For example, small ball seats yield large fluid flow restrictions. As a result, when stimulating zones, fluid flow restrictions in the tubing string will yield an inefficient production rate.
Therefore, there is a need for a more efficient system and method for isolating multiple zones of the wellbore.